The invention concerns generally the use of certain protocols and services for conveying certain types of information between the different nodes of a telecommunication network. Especially the invention concerns the transmission of multimedia-related information between a terminal of a cellular radio network and a store-and-forward type messaging center which has a network connection to at least one node computer of a fixed packet-switched network.
Multimedia is generally understood as the synchronized presentation of audiovisual objects to a user. It is typical to multimedia-related information that it may contain elements of highly different nature, like text, still images, simple graphical elements, video and sound.
MMS or Multimedia Messaging Service is a proposed way for arranging the delivery of messages containing multimedia-related information from one telecommunication device to another. With xe2x80x9cmultimedia-relatedxe2x80x9d information we mean both the actual payload data that represents presentable objects and the control information that tells a presentation device how to handle the payload data. According to the proposals, MMS should be applicable for conveying such messages to and from the terminals of packet-switched cellular radio networks such as GPRS (General Packet Radio Service) and the packet-switched parts of UMTS (Universal Mobile Telecommunication System) in a store-and-forward manner much like the SMS (Short Messaging Service) text messages are conveyed in the second generation digital cellular networks, e.g. GSM (Global System for Mobile telecommunications).
FIG. 1 illustrates some system aspects of a known proposal for arranging the transmission of MMS messages between two mobile terminals 101 and 102. In FIG. 1 each terminal is operating in a cellular telephone system of its own: terminal 101 is a UMTS terminal operating in a UMTS network 103 and terminal 102 is an enhanced GSM terminal operating in an enhanced GSM network 104. From both networks there is a connection to a GPRS network 105. The UMTS network 103 comprises a UTRAN or UMTS Terrestrial Radio Access Network 106 as well as a CN or Core Network 107. In the enhanced GSM network 104 a BSS or Base Station Subsystem 108 and an MSC or a Mobile Switching Centre 109 are shown. The detailed structure of the network elements is unessential to the present invention, but it is known that for example a UTRAN consists of a number of Radio Network Subsystems, each of which in turn comprises a Radio Network Controller and a number of Node Bs roughly corresponding to base stations. A BSS in turn comprises a Base Station Controller and a number of Base Transceiver Stations operating under it. Various mixed-mode cellular telephone systems are possible; for example the BSS 108 might operate under the same CN as the UTRAN 106. The terminals could also be exactly similar terminals operating close to each other in a single cell.
In FIG. 1 there is a connection both from the UTRAN 106 and from the BSS 108 to a corresponding SGSN or Serving GPRS Support Node 110 and 111. Both of these are in turn coupled, through the GPRS trunk lines, to a GGSN or Gateway GPRS Support Node 112 which also operates as an MMSC or a Multimedia Messaging Service Center. In analogy with the known SMS arrangements a terminal 101 may transmit an MMS message by identifying both the intended recipient""s terminal 102 and the MMSC through which the message is to be transmitted (actually the latter may even be left out if there is a default MMSC for each terminal). A Packet Control Unit or a corresponding functionality in the UTRAN 106 takes the MMS transmission and routes it through the current SGSN 110 to the MMSC 112 which stores the MMS message and commences the attempts for delivering it to the intended recipient. If there is an existing connection to the recipient""s terminal 102 the MMSC may deliver the message through the corresponding SGSN 111 and the BSS 108 to the terminal 102. If, however, the terminal 102 is temporarily shut off, out of coverage or otherwise unreachable, the MMSC retries the delivery at certain time intervals until either the message is successfully delivered or a timeout expires indicating that the message is obsolete and can be deleted undelivered. A positive or negative acknowledgement, depending on the success in delivery, may be returned to the transmitting terminal 101 if required.
A topic for discussion has been the most advantageous way of using the lower-level protocol layers and PDP Contexts (Packet Data Protocol) in the terminals and fixed network devices to convey the MMS messages. Somewhere at a relatively high level in the protocol stacks of both the terminals and the MMSC there must be an MMS-TP (Multimedia Messaging Servicexe2x80x94Transport Protocol) entity that uses the services offered by the lower level protocols to convey an MMS message first from the transmitting device to the MMSC and then further to the receiving device. Additionally the MMS messages must be mapped into PDP Contexts of certain type; the mapping will be closely related to the choice of lower protocol layers under the MMS-TP entity. We anticipate that network operators will require the MMS messaging to be distinguishable from other forms of packet-switched data transmission in order to arrange for a suitable charging scheme for the MMS services.
At least three prior art solutions have been proposed for conveying MMS messages. One of them is to have a PDP Type separately defined for MMS, and to set up a PDP Context of that type between a terminal and an MMSC each time an MMS message has to be conveyed in either direction. This approach has the drawback of requiring a considerable amount of completely new specification and standardization work. Additionally new PDP Types are only very reluctantly accepted to the already frozen standards. A second proposed prior art approach is to build the MMS messaging on top of the known IP or Internet Protocol PDP Type. The latter approach would require the GGSNs to reserve and allocate dynamic IP addresses to mobile users. The use of dynamic addresses is not efficiently combined to MMS services, and in any case using the IP PDP Type for MMS messaging would consume the scarce IP addresses and involve the whole complexity of allocating and maintaining IP addresses and dynamically configuring hosts. A terminal roaming in another network should in practice always use the MMSC of its home network, because there is no possibility of dynamically telling the IP addresses of other MMSCs to the terminal.
A third approach has been proposed in the Finnish patent application no. 990586 of the same applicant, which application is not available to the public at the time of filing this application. The third approach is based on the use of the OSP or Octet Stream Protocol as the supporting lower-level service for the multimedia-related information. The advantages of OSP comprise limited overhead information, avoidance of dynamic IP address allocation, minimal need for revision to existing specifications and flexible addition of future enhancements. However, it has been found out that even the use of OSP does not solve all problems related to the arrangement of FIG. 1: the implementation of the integrated GGSN/MMSC entity is quite complex, and the multimedia messaging service must be directly controlled by the operator responsible for the operation and maintenance of the fixed packet-switched network.
It is an object of the present invention to provide a feasible method and a corresponding arrangement for conveying MMS messages between terminals and MMSCs. It is an additional object of the invention that the proposed method does not require exhaustive respecification in the framework of existing standards and proposals. A further object of the invention is to minimize the required protocol overhead in the MMS traffic between the terminals and the MMSCs. An even further object of the invention is to provide means for distinguishing the MMS traffic from other types of packet-switched information transfer. Additionally it is an object of the invention that the drawbacks of the above-explained OSP solution are avoided.
The objects of the invention are met by using the OSP or Octet Stream Protocol, known as such, to carry a data stream comprising the required multimedia-related information, implementing the multimedia messaging center separately from the node computers of the fixed packet-switched network and coupling it to such a node computer through a network connection.
The method according to the invention is characterized in that it comprises the steps of
defining an octet stream protocol layer for the transmission of unstructured octet streams as a certain layer in a first protocol stack and a certain layer in a third protocol stack,
defining a network transmission protocol layer for the transmission of data between a first network device arrangement and a second network device arrangement,
defining a multimedia messaging transport protocol layer as a certain layer above said octet stream protocol layer in the first protocol stack and above said network transmission protocol layer in the second protocol stack and
exchanging multimedia-related information between the multimedia messaging transport protocol layer in a terminal arrangement and the multimedia messaging transport protocol layer in a first network device arrangement through the use of the octet stream protocol layer as well as other lower layers in the first and third protocol stacks and through the use of said network transmission protocol layer as well as other lower layers in the second and third protocol stacks.
Additionally the invention applies to a network device which is characterized in that its control block is arranged to
implement a network transmission protocol layer in a protocol stack for arranging the mutual exchange of information between network device and another network device,
implement an octet stream protocol layer in said protocol stack for the transmission of unstructured octet streams between the first network device arrangement and a terminal arrangement,
convert multimedia-related information coming from the other network device arrangement through said network transmission protocol layer into a format to be transmitted to the terminal arrangement through said octet stream protocol layer and
convert multimedia-related information coming from the terminal arrangement through said octet stream protocol layer into a format to be transmitted to the other network device arrangement through said network transmission protocol layer.
The invention resembles the above-explained third solution in that the Octet Stream Protocol or OSP is used. However, instead of placing the MMS-TP protocol entity directly on top of the OSP entity in a GGSN, a conversion between OSP and some general network protocol is set up in the GGSN and said general network protocol is used to couple the GGSN to the MMSC, which may even very distantly located.
A PDP Context activation procedure between a terminal and a MMSC is required to enable the transmission of MMS messages in the framework of OSP. The device that initiates the activation procedure transmits an Activate PDP Context Request that contains a set of parameters that are required to identify and define the desired PDP Context. In the case of terminal-initiated PDP Context activation the SGSN may need to select the appropriate GGSN on the basis of the parameters contained within the activation request and possibly using also previously stored information about the home location of the terminal. On the basis of the information contained within the activation request the GGSN directs it further to a MMSC functionality. A multitude of network elements like routers, firewalls and so on may take part in the transmission of messages between the GGSN and the MMSC.
After the PDP Context setup has been accomplished, MMS messages are conveyed as an octet stream by using either the octet mode, where the OSP protocol entity applies a packet assembly/disassembly function, or the block mode where no separate packet assembling or disassembling is performed.
The invention has all the advantageous features of using OSP as the bearer for MMS, like minimized protocol overheads, complete separation of the MMS-related PDP Context from all other PDP Contexts even without defining a new PDP Type and avoidance of dynamic allocation of IP addresses. Additionally the invention simplifies the structure and operation of the MMSC compared to the integrated GGSN/MMSC solution and enables complete independency of the MMSC from the GPRS or other fixed packet-switched network.
The utilization of an unstructured octet stream between a terminal and a GGSN as well as a network connection between the GGSN and a MMSC enables the operators to direct the MMS-carrying PDP Contexts of desired users very freely; for example the MMSC residing in the user""s home network can be used. On the other hand, operators may also allow any MMSCs to be used, but this may restrict the service to the mobile-originated alternative only. In any case the control possibilities are much more flexible than in the IP-based prior art solutions. A terminal may even select a desired MMSC by using a certain predefined parameter in an Activate PDP Context Request.